Carbon nanostructures have received a great deal of interest since their discovery. It has been suggested that carbon nanostructures may have important applications in electronics, in materials sciences, and in a number of additional fields. As used in this disclosure, a carbon nanostructure comprises a structure formed from chemically bonded carbon atoms, with or without impurities or intentionally added materials incorporated in the carbon structure or adjacent to the carbon structure. Carbon nanostructures include particularly carbon nanotubes in which carbons atoms are arranged in generally a hexagonal ring with a series of such rings arranged along a linear or curved axis side-by-side to form a tube structure. Carbon nanotubes may be single walled or multiple walled. Single wall nanotubes include a single hexagonal arrangement of carbon atoms arranged side-by-side with other such hexagonal rings, while multiple walled nanotubes are made up of a series of inner hexagonal rings and a series of one or more layers of outer hexagonal rings.
Despite the interest in carbon nanostructures and the potentially important uses for such structures, the practical application of carbon nanostructures in products has been slowed by the difficulty in manufacturing such structures. Two general types of processes have been employed to produce or isolate carbon nanostructures. One process type uses a plasma arc between carbon electrodes. U.S. Pat. Nos. 5,482,601 and 5,753,088 describe such carbon plasma arc processes for producing carbon nanotubes. Another process type involves simply isolating naturally formed, self-assembled carbon nanotubes from graphite and soot. Such an isolation process or refinement process for carbon nanotubes is described in U.S. Pat. No. 5,560,898.
The prior processes for producing or isolating carbon nanotubes have been found to produce only small quantities of carbon nanotubes of inconsistent quality. The low quality carbon nanotubes produced or isolated by the prior methods commonly included metal or other atoms incorporated in the carbon structure. These impurities incorporated in the walls of the carbon nanotubes may have a negative impact on the qualities and properties of the nanotube and may render it unsuitable for an intended purpose.